Semiconductor lasers, as well as other optoelectronic devices must be evaluated for long-term reliability. Often this entails evaluation of the current required for lasing, the threshold current, before a test operation at an elevated temperature; and after the test operation. This is often referred to as ‘burn-in’ or ‘purge’ testing.
During purge testing, the laser is operated for a predetermined time at the elevated temperature; and is driven at a relatively high bias current. After this testing is completed, the threshold current is re-evaluated. From these data, a fairly accurate correlation may be made between any changes in the threshold current due to the purge testing and the rate that the laser degrades over time. This degradation is typically referred to as the age-rate of the laser, and may be used in the pass/fail analysis of lasers in a manufacturing setting.
Known methods for purge testing lasers include the use of an external photodetector with intermediate optics, which forms a test apparatus; and the use of a rear facet monitor-detector. While these known methods are useful in accomplishing the desired end, there are certain drawbacks to their use. To this end, there is an attendant cost associated with the test apparatus and its method of testing. Moreover, the total yield in production depends on the individual yields of the elements, and failure of any one element can impact the overall yield of a product. These yields include a purge yield associated with the lasers; and an electro-optical test yield of the lasers.
What is needed, therefore, is a method for evaluating the age-rate of a laser that overcomes at least the drawbacks of known methods described above.